HYDROGEN SOLUBILITY LIMITS IN EXCEL, AN EXPERIMENTAL ZIRCONIUM-BASED ALLOY

Specimens of Excel alloy were charged to different hydrogen concentrat ion levels from the gas phase. Two different techniques were used to d etermine the hydride dissolution and precipitation I nucleation temper atures on heatup and cooldown of the specimens. These were the differe ntial scanning calorimetry (DSC) and dynamic elastic modulus (DEM) tec hniques. Hydrogen concentration in the specimens was measured using ho t vacuum extraction methods. The hydrogen solubility limit in Excel is found to be higher than for Zircaloy-2 or Zr-2.5wt.%Nb. Similar to ot her zirconium alloys, a strong hysteresis is observed. The hydride dis solution temperatures measured by both DSC and DEM techniques are in g ood agreement and do not depend on the experimental conditions. Howeve r, the precipitation temperatures are very sensitive to T-max (the hig hest temperature reached in the heating/cooling cycle). The reason for the difference in solubility between Excel and, particularly, Zr-2.5w t.%Nb is explored.